The present invention relates to a method of producing an exhaust port arrangement of a cylinder head installed with a port liner in its exhaust port passage.
Various techniques have been proposed to reduce air pollutants such as hydrocarbon and carbon monoxide in the exhaust gases emitted from the automobiles. Among such techniques, it has been practiced to mount a thermal reactor and/or a catalyst in the exhaust system of an internal combustion engine. The efficiencies of the thermal reactor and the catalyst depend on the temperature of exhaust gas, so that it is necessary to minimize the heat loss in the exhaust system to maintain the exhaust gas at an elevated temperature.
A conventional internal combustion engine is thus installed with a port liner in an exhaust port passage of a cylinder head upon casting of the cylinder head to form a heat insulation layer on the exterior surface of the port liner. Such method includes the steps of preparing a core comprising an elongate tubular port liner having a cavity to serve as an exhaust port when installed in the exhaust port passage, a mass of moulding sand closely filled in the cavity and an elongate tubular layer of moulding sand formed on the exterior surface of the port liner to form thereon a heat insulation layer.
Such steps, however, have a drawback of poor productivity which is caused by the fact that it needs a considerable time until the mass of green moulding sand cures completely because the mass must be mainly heated through the tubular layer and the port liner and further because the amount of heat supplied to the tubular layer should be maintained under a predetermined level which assures proper curing of the tubular layer.